1. Field of the Invention
The present invention relates to an insulator composition used as an electrical insulating material in a laminated electronic part, for example, such as a thick film printed multilayered circuit board, insulator paste comprising a mixture of the insulator composition and an organic vehicle, and a laminated electronic part such as a multilayered circuit board comprising an insulating layer obtained by burning the insulator paste.
More specifically, the present invention relates to an improvement for making the insulator composition or insulator paste sinterable at relatively low temperature, and for making it possible to freely change the thermal expansion coefficient of an insulating layer obtained by burning the insulator composition or paste while maintaining a low dielectric constant.
2. Description of the Related Art
As a result of recent developments in semiconductor integrated circuit devices such as IC and LSI, decreases in size of various electronic apparatus and increases in density thereof have rapidly proceeded. Accordingly, the circuit board for mounting the semiconductor integrated circuit devices thereon has been required to have a smaller size and higher density, thereby advancing the formation of fine and multilayered electric wiring on the circuit board.
This multilayered circuit board is classified into the following types on the basis of the manufacturing method thereof.
(1) A multilayered circuit board obtained by preparing a plurality of ceramic green sheets for forming an insulator layer, forming a conductor pattern for forming a conductor layer on each of the ceramic green sheets, laminating the plurality of ceramic green sheets on each of which the conductor pattern is formed to form a laminated product, and then burning the laminated product.
(2) A sequential burning type multilayered circuit board obtained by a printing technique in which the step of coating insulator paste for an insulator layer on a ceramic sintered sheet or ceramic green sheet as a base material by printing includes burning in this step, and then coating a conductor paste for a conductor layer by printing, and the burning is repeated.
(3) A simultaneous burning type multilayered circuit board obtained by a printing technique in which the steps of coating insulator paste for an insulator layer on a ceramic sintered sheet or ceramic green sheet as a base material by printing and coating a conductor paste for a conductor layer by printing are repeated to obtain a laminated product, and then the resultant laminated product is integrally burned.
On the other hand, it is known that the propagation velocity of a signal in a conductor decreases as the dielectric constant of a peripheral material increases, and an electric insulating material for high-velocity propagation is required to have a low dielectric constant.
A known example of such electric insulating materials having a low dielectric constant is cordierite. The cordierite is also known as a material having a low thermal expansion coefficient.
In the above-described multilayered circuit board (2) or (3), it is important to match the thermal expansion coefficient of the board with the thermal expansion coefficient of the insulator layer. Mismatching between these thermal expansion coefficients causes the problem of warping the resultant multilayered circuit board. Particularly, the use of alumina as the base material, and cordierite as the insulator layer causes significant warping because cordierite has a low thermal expansion coefficient.
The conductor which constitutes the conductor layer formed for providing circuit wiring in the multilayered circuit board generally has a thermal expansion coefficient of as high as 10 ppm/xc2x0 C., thereby possibly causing mismatching between the thermal expansion coefficients of the conductor layer and the insulator layer in the multilayered circuit board (1), and mismatching between the conductor layer, the base material, and the insulator layer in the multilayered circuit board (2) or (3). Such mismatching between the thermal expansion coefficients also cause the problem of warping. The degree of warping depends upon the density of circuit wiring provided by the conductor layer.
Therefore, the material for the insulator layer is desired to have a thermal expansion coefficient which can easily be changed so as to decrease mismatching of thermal expansion coefficients as much as possible according to a circuit design comprising the base material and the conductor layer.
Accordingly, it is an object of the present invention to provide an insulator composition and insulator paste which can be used as materials of an insulator layer satisfying the above desire. Another object of the present invention is to provide a laminated electronic part such as a multilayered circuit board obtained by using the insulator paste.
The present invention is directed to an insulator composition comprising a crystallized glass composition containing SiO2, MgO and CaO as main components, and Al2O3, an amorphous silicate glass composition, and a ceramic composition. In order to solve the above technical problems, the crystallized glass composition comprises the main components at a composition ratio by weight % (SiO2, MgO, CaO) in the region surrounded by point A (30, 25, 45), point B (30, 5, 65), point C (45, 5, 50) and point D (45, 25, 30) shown in the ternary composition diagram of FIG. 1.
The crystallized glass composition can be generally obtained by melting raw materials, and then rapidly cooling the resultant melt. However, in the specification of the invention, the term xe2x80x9cthe crystallized glass compositionxe2x80x9d means a xe2x80x9cglass composition having a crystal phasexe2x80x9d and/or a xe2x80x9cglass composition having the ability to precipitate a crystal phase by heat treatmentxe2x80x9d.
In the present invention, the crystallized glass composition preferably comprises about 5 to 28 parts by weight of Al2O3 based on a total of 100 parts by weight of the main components.
In heat treatment of the crystallized glass composition at a temperature higher than the crystallization temperature, at least one crystal phase of merwinite (Ca3MgSi2O8), monticellite (CaMgSiO4), calcium silicate (at least one of CaSiO3, Ca3Si2O7, Ca2SiO4 and Ca3SiO5), gehlenite (Ca2Al2SiO7) and diopside (CaMgSi2O6) is preferably precipitated.
Although the above specified crystal phases are generally precipitated after heat treatment, the crystal phases are partially precipitated before heat treatment in some cases. Besides these crystal phases, in some cases, the crystallized glass composition further contains another crystal phase. Such another crystal phase is also precipitated after heat treatment or partially precipitated before heat treatment.
The crystallized glass composition may further comprise 0 to about 20 parts by weight of B2O3, and 0 to about 5 parts by weight of at least one of Li2O, K2O3 and Na2O.
In the present invention, in a preferred embodiment, the amorphous silicate glass composition comprises borosilicate glass. In this case, the borosilicate glass preferably contains about 75 weight % or more of SiO2. The borosilicate glass preferably contains SiO2, B2O3 and K2O3 at a composition ratio by weight % (SiO2, B2O3, K2O) in the region surrounded by point E (75, 25, 0), point F (75, 20, 5), point G (855, 10, 5) and point H (85, 15, 0) shown in the ternary composition diagram of FIG. 2.
In the present invention, in a preferred embodiment, the ceramic composition comprises at least one of alumina (Al2O3), forsterite (Mg2SiO4) and quartz (SiO2).
The insulator composition of the present invention preferably comprises about 50 weight % or less of ceramic composition.
In a specified embodiment of the present invention, the thermal expansion coefficient of the crystallized glass composition after sintering is set to about 7 ppm/xc2x0 C. or more, and the thermal expansion coefficient of the amorphous silicate glass composition after sintering is set to about 4 ppm/xc2x0 C. or less so that the thermal expansion coefficient of the resultant insulator composition after sintering is in the range of about 2 to 12 ppm/xc2x0 C.
In the insulator composition of the present invention, besides a crystal phase formed by the ceramic composition, at least one crystal phase of merwinite (Ca3MgSi2O8), monticellite (CaMgSiO4), calcium silicate (at least one of CaSiO3, Ca3Si2O7, Ca2SiO4 and Ca3SiO5), gehlenite (Ca2Al2diopside (CaMgSi2O6) is preferably precipitated after burning.
The insulator composition is generally powdery, and is mixed with an organic vehicle to form paste. In order to form an insulator layer, for example, the insulator paste is coated as a thick film on an appropriate base material by printing, and then burned.
Therefore, the present invention is also directed to insulator paste comprising the insulator composition and an organic vehicle, and a laminated electronic part such as a multilayered circuit board comprising an insulator layer obtained by burning the insulator paste. The laminated electronic part of the present invention has a structure in which the insulator layer and the conductor layer obtained, e.g., by burning a silver-system, copper-system or gold-system conductor paste, are laminated.